Every organization has at least one project. Projects are naming conventions used to designate functional teams (such as Frontend, Backend, Mobile, DevOps, etc.), but can also represent any open-ended product, initiative or category of work. An example of a category of work that doesn't directly conflate a specific team would be something called "API Documentation".
An Epic is a collection of Stories (individual pieces of work) that together make up a larger initiative that your Workspace is working on. An example of a large initiative would the release of your organization's first mobile app. Due the nature of this, Epics have a start and an end date. Oftentimes an Epic can be a place for multiple Project teams to work together toward a shared goal.
Epics and Projects are not similar, but there is a relationship between them in that an Epic can be indirectly associated with a Project (or Projects, as the case may be) through the Stories in that Epic.